It has been the practice to monitor intracranial pressure of patients suffering from severe brain injuries for many years. Several different structures have been proposed and adopted for this purpose. The structures generally include a shaft, in the form of a bolt or screw, having a central passage for coupling fluid pressure from the subarachnoid space to a pressure transducer which can be selectively connected to a tube adapted to be connected to the shaft. The shaft extends through an opening in the scalp, through the three layers of the skull, i.e., the outer table, the diploe, and the inner table, and through the dura mater and the arachnoid to the subarachnoid space.
One prior art subarachnoid screw for monitoring intracranial pressure includes a standard luer lock and a hexagonal collar for insertion at the proximal end of the screw. Threads on the distal end of the screw fit a quarter inch twist drill hole. A glass wool wick may be placed in a lumen of each screw before insertion of the screw to prevent occlusion at the tip of the screw. The screw is inserted by making a twist drill hole in the skull of the patient through a scalp incision under local anesthesia. The thereby exposed dura mater is nicked with a knife under direct vision by the surgeon and removed with a small angled currette, to open the dura and the arachnoid. The screw is threaded into the twist drill hole with a hexagonal screwdriver to a location that places the tip of the screw slightly below (preferably 1 mm.) the dura surface. The incision in the scalp is closed around the shaft screw with sutures and a small sterile dressing is placed around the shaft. The screwdriver is formed as a shaft having a pair of diametrically opposed tines which engage the hexagonal collar on the screw shaft. The screwdriver includes a pair of diametrically opposed rods which form a handle enabling the screwdriver to be turned by hand.
The aforementioned prior art structure, however, does not remain securely attached to the skull during the usual period of time for which it is used for intracranial pressure monitoring, a period most commonly from three to seven days. The thread has insufficient length to be securely screwed into most skulls. The screw must be attached to a stopcock, which when manipulated causes movement and loosening of the screw. The combination of the screw and stopcock produces a device which extends for a considerable distance above the scalp and is therefore easily jarred loose.
A further intracranial subarachnoid pressure monitoring device includes a bolt having a threaded section screwed into the skull of the patient. At the end of the threaded portion is a smooth portion having a diameter less than the threaded portion and containing an orifice for coupling fluid from the subarachnoid space into a passage extending longitudinally through the bolt. At the other end of the threaded portion is a radially extending flange that serves as a seal for a twist drill hole that is made by the surgeon into the skull. Longitudinally spaced along the bolt from the flange is a local widening for receiving a wrench which is used to drive the bolt into the skull. Extending from the local widening is a stub shaft which forms a female adapter for intravenous tubing. The intravenous tubing is connected to a pressure transducer, whereby the fluid pressure coupled through the bolt channel is coupled to the pressure transducer.
The bolt is inserted by making an incision through the scalp to the skull and then boring a hole through the skull, without penetrating the dura mater. The bolt is placed into a bolt handle and then screwed into the bored hole until the bolt flange closes snugly against the skull outer table to enhance stability. The dura mater is then perforated several times with a wire probe to insure communication of the passage in the bolt with the subarachnoid space. The incision in the scalp is then closed with sutures. Thereafter, the intravenous tubing is connected to the bolt.
This prior art structure has a lower profile than the previously described prior art device. However, the flange is not adjustable to accommodate skulls having differing thicknesses and the bolt requires a large scalp incision for insertion.
Both of these generally used prior art screws or bolts frequently become occluded by a blood clot or dura mater fragments.
A further prior art intracranial probe for monitoring subarachnoid pressure has a self-tapping thread capped intracranial end capped by an end plate with side ports providing fluid communication between the intracranial space and a tube leading to a monitoring device. Prior to inserting this prior art probe into the subject, a formal burr hole is made in the skull. The hole has a relatively large diameter, about 3/4 inch, and requires significantly more operative effort than a small twist drill hole.
It is, accordingly, an object of the present invention to provide a new and improved subarachnoid probe for monitoring intracranial pressure.
A further object of the invention is to provide a new and improved probe for enabling intracranial pressure in the subarachnoid space to be determined more accurately over the required time period.
Still a further object of the invention is to provide a probe for enabling intracranial pressure in the subarachnoid space to be determined, wherein the probe is stably mounted in the skull for the required period of time.
Still a further object of the invention is to provide a new and improved probe for enabling intracranial pressure in the subarachnoid space to be determined, wherein the probe is capable of accommodating skulls having different thicknesses.
Still a further object of the invention to provide a new and improved probe for enabling intracranial pressure in the subarachnoid space to be determined, wherein the probe includes openings into a passage so that the likelihood of occlusions is considerably reduced.